Presidents, prime ministers - how universally they hate to step down from power. Long after most of their people and colleagues wish they would go, they hang on, convinced that the country still needs them. Fraser Grace's play about Zimbabwe in 2001, currently on stage in London, resonates with Britain in 2006. We all have conversations about what on earth Blair is thinking. What's in his head? And we know we don't have a clue. But when it comes to the same conversation about Mugabe, the old African stereotypes come up and we say that he's mad.

Political theatre is now more fashionable than ever, from the Tricycle's tradition of tribunal plays to David Hare's plays at the National on the Iraq war or the the railways. Robert Mugabe, routinely demonised by the British media as a larger than life African tyrant - Idi Amin with brains - was an obvious dramatic target.

Grace took a bold leap based on an article by a journalist with a history of unfriendliness to southern African liberation movements. The headline was: "Paranoid Mugabe dines with a ghost." Mugabe was depressed and being treated by a white psychiatrist, it said. That story became the play Breakfast with Mugabe. This was tempting but perilous territory for an imaginative writer, and only someone who had never been to Zimbabwe would probably have dared to go there.

I had breakfast with Mugabe myself once, in the late 1980s. Mugabe was then, with Julius Nyerere of Tanzania, one of Africa's leading intellectuals to hold power in the post-colonial period. He was courteous and as clever as his academic record of degrees gained in prison suggested. His conversation was about world economic trends and new books, though inevitably mostly about the hidden war that apartheid South Africa was then waging against Angola, Mozambique and other frontline states. I had often been to Angola, the war's centre, where American funding, logistics and propaganda were critical to South African military offensives. Mugabe wanted to hear the story from the ground.

The president was on one of his unproductive visits to Margaret Thatcher's Britain to ask for support against the death and devastation from South Africa. It was not easy for him to ask anything of Britain, so raw was the old wound of the colonialism that had shaped his life. But economic and political destabilisation were crippling the country and its neighbours, and political assassinations of African National Congress members were terrorising the region.

Mugabe's Zimbabwe took the considerable risk of hosting a conference of South African children tortured by the apartheid regime, and exiled ANC leaders came to Harare to meet lawyers, churchmen and township activists from South Africa. And it was in Harare that Castro declared he would keep Cuban soldiers in Angola until the end of apartheid. These things fired the courage of the South African resistance and explain why today's Mugabe is still a hero in South Africa despite economic collapse, crude repression and the flight of thousands of Zimbabweans to South Africa.

Grace's Breakfast with Mugabe, like the article, has Mugabe haunted by the spirit of the charismatic Josiah Tongogara, the military leader of the Zanla guerrilla army in Zimbabwe's struggle. CIA briefings said that Tongogara was killed by his own side because he was a rival to Mugabe. The memoirs of the former prime minister Ian Smith told the same tale. To choose to believe the western version was a political choice in the cold war climate of 25 years ago. As a device in the play, it allows the bullying white psychiatrist to pronounce that guilt over the death of Tongogara and the idealism he represented are at the root of Mugabe's anxiety attacks.

In a clever twist, Grace's psychiatrist is also a tobacco farmer. His straight-talking with the president brings him his own comeuppance, and we see him as a broken man sitting in his farm, looking on as Mrs Mugabe decides that it will be just right for one of her nieces.

An outing to see this play should be twinned with one to see the current production of The Exonerated - true stories of miscarriages of justice in America. Power corrupts in small-town police stations in the midwest as easily as in any state house in Africa. But The Exonerated also shows us the heroic resistance modest people are capable of.

· Breakfast with Mugabe is at the Duchess Theatre, London; The Exonerated is at the Riverside Studios, London.

· Victoria Brittain is the author of Hidden Lives, Hidden Deaths: South Africa's Crippling of a continent, and Death of Dignity: Angola's civil war.